1. Field of the Invention
The present invention relates to an air fuel mixer for the combustor of a gas turbine engine, and, more particularly, to an air fuel mixer for the combustor of a gas turbine engine which includes slots at a downstream end of the mixing duct in order to improve mixing eddies emanating from the mixing duct and thereby reduce dynamic pressures in the combustor.
2. Description of Related Art
The present invention involves an improvement to air fuel mixers, and specifically to air fuel mixers previously filed by the assignee of the present invention. These air fuel mixers include U.S. Pat. No. 5,165,241, entitled "Air Fuel Mixer For Gas Turbine Combustor", U.S. Pat. No. 5,251,447, entitled "Air Fuel Mixer For Gas Turbine Combustor", and Ser. No. 08/170,969, entitled "Dual Fuel Mixer For Dry Low NOx Gas Turbine Combustor". As seen therein, each of these air fuel mixers includes a mixing duct, a set of inner and outer counter-rotating swirlers adjacent the upstream end of the mixing duct, and a hub separating the inner and outer swirlers to allow independent rotation thereof. Various manners of injecting fuel into the mixing duct are described in each patent/patent application. Accordingly, high pressure air from a compressor is injected into the mixing duct from the swirlers to form an intense shear region and fuel is injected into the mixing duct so that the high pressure air and the fuel is uniformly mixed therein so as to produce minimal formation of pollutants when the fuel/air mixture is exhausted out the downstream end of the mixing duct into the combustor and ignited.
While the aforementioned air fuel mixers have greatly increased mixing of fuel and air, and correspondingly reduced emissions produced from the burning thereof, it has been found that turbulent eddies are shed from the exit plane (or downstream end) of the mixing duct. In particular, it has been found, as depicted in FIG. 1, that such turbulent eddies are toroidal in shape (when viewed in cross-section) and have centerlines circular in nature which are convected downstream. The eddies are formed as the high velocity premixed fuel/air flow draws in and mixes with the recirculating hot burnt gases. The main problem with such toroidal eddies is that they have characteristic shedding frequencies which can couple with the fuel or air supply systems to set up a resonance. Accordingly, a need has arisen to modify the character of the eddies emanating from the exit of the mixing duct while preserving the ultra low NO.sub.x emission characteristic of the mixer.